The Jimmy Garoppolo-less San Francisco 49ers visit the Los Angeles Chargers in Week 4, and these five points will be essential in the Niners pulling off an upset.

It shouldn't come off as a shock the odds makers are all but writing off the San Francisco 49ers in Week 4 as they visit the 1-2 Los Angeles Chargers at the StubHub Center in Southern California. Currently, Odds Shark has the Niners listed as 10-point underdogs, which is the largest spread of any games this week.

Most of that, of course, stems from the season-ending ACL tear to quarterback Jimmy Garoppolo, which thrusts second-year pro C.J. Beathard into a starting role once again.

Beathard struggled in this capacity his rookie season, finishing 31st out of 32 qualifying quarterbacks with a 69.2 passer rating over seven games played. Granted, that was when he was a fresh-faced first-year player, and the talent surrounding Beathard wasn't anywhere as developed or cohesive as it is right now.

That said, Beathard and Co. will have a tough time going up against the Chargers.

Los Angeles quarterback Philip Rivers has his own arsenal of weapons, not unlike what the 49ers faced in Week 3 during their road loss to the Kansas City Chiefs. Second-year wide receiver Mike Williams is coming into his own, developing as the complementary piece to the already-established Keenan Allen. And running back Melvin Gordon is, perhaps, one of the more unheralded dual-threat tailbacks in the NFL today.

It's possible, perhaps likely, the 49ers defense winds up being the key X-factor for San Francisco, as head coach Kyle Shanahan's squad looks to get back to the .500 mark.

Can the 49ers Defense Bounce Back?

The Chargers offense might not be quite as potent as that of K.C., but facing it is still a daunting task for the Niners. L.A. comes into the contest with the No. 8-ranked scoring offense, also averaging 6.9 yards per play.

The Chiefs averaged 5.6 yards per play in their 38-27 victory over San Francisco.

Two major problems plagued the Niners last week -- missed tackles and a porous secondary. Through three weeks, the 49ers have missed a whopping 43 tackles, according to Pro Football Focus, which is the most out of any defense this season. Linebacker Reuben Foster, who made his 2018 debut after his two-game suspension to open up the year, had six missed tackles during the game after missing no more than 10 his rookie year.

If that trend continues, San Francisco is in trouble.

The secondary might also be in trouble, particularly with cornerback Richard Sherman (calf) ruled out and safety Jaquiski Tartt (shoulder) doubtful. Defensive backs Antone Exum and Adrian Colbert are also questionable.

Rivers will likely target the Niners' banged-up secondary a lot Sunday, putting pressure on both the fill-in options and the relatively absent 49ers pass rush to deliver.

C.J. Beathard vs. the Blitz

Also according to Pro Football Focus, both the Chargers' losses this season have come when their defense blitzed less than the league average.

Beathard wasn't effective against pressure last season, tossing for a passer rating of 66.0 when blitzed, compared to 83.9 when not facing pressure at all. This number improved as 2017 drew on, so the hope is Beathard's full year within the league adds to the maturation and ability handling the extra rushing pressure from L.A.

Oh, and it's a bonus the Chargers will be without their top edge rusher, Joey Bosa, who remains out with a foot injury.

A Banged-Up 49ers Rushing Attack

No. 1 running back Matt Breida, who is leading the league with an average of 8.6 yards per carry, suffered a hyper-extended knee in Week 3 but returned, is listed as questionable on San Francisco's injury report. He was limited in practice on Wednesday and Friday during the week, fully participating on Thursday.

Shanahan indicated Breida would be a game-time decision, understanding it's still early in the season and how Breida will be a major factor in the 49ers offense from this point onward.

To complicate the issue, No. 2 running back Alfred Morris (knee) is also listed as questionable. He didn't practice on Wednesday and was limited on both Thursday and Friday. If both players are unable to go, which seems unlikely, the 49ers would be forced to rely heavily on special teams ace Raheem Mostert as the primary ball carrier.

One would guess both Breida and Morris are made available for the game but have the NFL's equivalent to a "pitch count" -- a limited number of carries for each, which puts more pressure on Beathard and the passing game.

#49ers banged up RBs Matt Breida (knee) and RB Alfred Morris (knee) are both in good positions to play, sources say. Breida was trending up late in the week, while Morris should be good, provided he has a good warmup vs. the #Chargers.

When Do the 49ers Wide Receivers Show Up?

Tight end George Kittle leads the 49ers in both receptions (12) and receiving yards (191) on the season. That's great for Kittle and that particular aspect of the game. But it doesn't reflect well on the Niners' wide receivers, who have yet to make a substantial impact in 2018.

Wide receivers Pierre Garçon and Trent Taylor each have seven receptions apiece, but neither has crested 100 yards on the season. Over three weeks and with Garoppolo mostly at the helm, this is concerning. Sure, in nearly two of those games, No. 1 wideout Marquise Goodwin was sidelined with a leg injury. But that doesn't change the fact the Niners receiving corps hasn't been much of a factor on the young season.

The Chargers are minus cornerback Jason Verrett (Achilles) this season, although rookie safety Derwin James is a player worth keeping an eye on as the 49ers look to get their wide receivers involved more in Week 4.

Those Damned Yellow Flags

OK, so a number of the penalties accepted against the 49ers in Week 3 was pretty ludicrous. But that doesn't change the fact the Niners were flagged a whopping 14 times for 147 yards in their loss to the Chiefs. San Francisco needed to play a near-perfect game on the road, and the context hasn't changed much now in L.A.

Through three weeks, the 49ers are tied for fourth most penalties in the league with 26. Outside of the Buffalo Bills (28 penalties accepted), all the other teams with more than San Francisco have substantially better rosters than what the Niners will carry into the StubHub Center on Sunday.

Simply put, Shanahan and Co. can't afford yet another penalty-ridden contest on the road against what appears to be, on paper, a vastly superior opponent.

Moderately improved discipline would vastly improve the Niners' chances for pulling off an upset in Week 4. Those frustrating pre-snap penalties would negate putting added pressure on Beathard and his receiving targets if eliminated. And the 49ers' suspect defense can ill-afford to gift the Chargers additional yardage on the other side of the ball.

It isn't as if L.A. needs the help here.

The 49ers and Chargers kick off at 4:25 p.m. ET on Sept. 30 from the StubHub Center in Carson, California.

Peter Panacy has been writing about the 49ers since 2011 for outlets like Bleacher Report, Niner Noise, 49ers Webzone, and is occasionally heard as a guest on San Francisco's 95.7 FM The Game and the Niners' flagship station, KNBR 680. Feel free to follow him, or direct any inquiries to @PeterPanacy on Twitter.

The views within this article are those of the writer and, while just as important, are not necessarily those of the site as a whole.

This site is neither endorsed, nor sponsored by, nor affiliated with San Francisco 49ers or NFL Properties LLC. 49ers is a registered trademark of the San Francisco 49ers LLC. All teams and players mentioned are registered trademarks of the NFL and its respective teams. The use of any team names, words, trademarks, logos or photos have been used for descriptive purposes only. The content and information from other sites is the property of their respective owners. Player and team photos used with permission from USA TODAY Sports Images.